The following is an overview of some preliminary key results and trends from our camera nest data and satellite tracking data so far. Our data analysis is ongoing, so watch this space for further updates on our findings…
Nesting habitats differ within and among sites and species
In Barmah-Millewa Forest and parts of the Macquarie Marshes, both Australian white ibis (Threskiornis molucca) and straw-necked ibis (Threskiornis spinicollis) prefer to nest in tall common reed (Phragmites australis). Both prefer reed beds with ‘water views’ in the centre of regularly inundated wetlands.
Royal spoonbills (Platalea regia) prefer to nest in giant rush (Juncus ingens) surrounded by water at Barmah-Millewa Forest, however do nest in trees at other sites. Straw-necked ibis in Barmah-Millewa Forest will also nest in giant rush.
Motion-sensing and time-lapse cameras set up on nests of Australian white ibis, straw-necked ibis and royal spoonbills collected data on egg and chick survival and mortality.
Egg hatching rates are low and vary between species
The combined egg hatching rates for all three species are low (30-60%). Royal spoonbill eggs are more likely to survive to hatching than straw-necked ibis eggs, while Australian white ibis eggs are the least likely to survive to hatching.
Most egg mortality is driven by predation or nest abandonment
Most predation events in Barmah-Millewa Forest are in daylight by native bird species, such as purple swamp hen (Porphyrio porphyria), Australian raven (Corvus coronoides), swamp harrier (Circus approximans), whistling kite (Haliastur sphenurus) and white-bellied sea eagle (Haliaeetus leucogaster). Anecdotally, predation by feral animals such as pigs, foxes and cats is more of a problem in other breeding sites like the Macquarie Marshes.
Chick survival rates in the nest are high
Once hatched, chick survival rates until leaving the nest are generally high and similar among the three species (88-92%). Future analyses will explore how nest exposure, parental behaviour and disturbance affect both egg and chick survival and mortality.
Satellite transmitters were attached to five straw-necked ibis adults from the Macquarie Marshes, and five adults and ten juveniles from Barmah-Millewa Forest. The following are an overview of the highlights and trends our tracked birds have shown so far…
Northern (birds from the Macquarie Marshes) and southern birds (Barmah-Millewa Forest) are mixing and using some of the same sites and routes. It’s unknown whether straw-necked ibis within Australia are one integrated population or geographically different populations. The 2016-2017 breeding season may be considered unusual with the extent and duration of flooding that occurred in eastern Australia; this will need to be investigated with satellite tracking in subsequent years and with more birds.
Common ‘flyways’ or movement corridors for separate birds/groups
Six of the ten adults and three juveniles have travelled along a common northeast-southwest route in different directions. This route corresponds to zones/boundary lines in maps of average climatic conditions such as rainfall and evapotranspiration.
Key foraging and stopover points and regions
Different birds have been using the same sites to forage and stopover at different times. Some birds have also returned to sites or ‘re-used’ sites. This has been apparent in the mid-Lachlan River near Condonblin, NSW (see satellite image below).
‘Paired’ habitats for roosting and foraging
The ideal foraging habitats have remnant vegetation with trees for roosting, adjacent to native or agricultural foraging habitats.
Movement associations with weather and season
Birds undertaking longer-distance movements have shown similar departure times and departure dates to each other; this is probably associated with thermals. Weather changes such as temperature drops, rainfall and shifts in wind direction, have also been triggering long-distance movements. All birds ceased long-distance movements and ‘settled-down’ in Autumn 2017; the movements of birds within their wintering areas is highly localised, but the location of wintering areas varies between birds.